The overall goal of this proposed research is to contribute to the molecular understanding of the mechanism of genetic recombination. The approach will involve the investigation of the physical, biochemical, and enzymatic properties of purified proteins which are known to be involved in the biological recombination process. The focus of these studies will be on the E. coli recA protein, and the interaction with its nucleic acid substrates, as well as the interaction with other proteins involved in recombination, such as SSB protein, recBC, and DNA helicases. The overall objective of these studies is to understand, at the physical mechanistic level, how these proteins interact with each other and with their nucleic acid substrates to produce a recombinant DNA molecule. The approaches to be used include physical investigations of the structural equilibrium and kinetic aspects of binding of recA protein to nucleic acid substrates and of the mechanism of recA protein catalyzed reactions such as DNA renaturation and DNA strand assimilation; biochemical studies of mutant recA protein variants, of proteolytic fragments of recA protein and of truncated recA gene products; and physical and enzymatic studies of the interaction of recA protein with other proteins such as SSB protein, recBC, and DNA helicases.